Preheat your oven to 350°F (175°C). Prepare two 9x2 inch round cake pans by greasing and flouring them.

In a medium mixing bowl, whisk together the cake flour, baking powder, baking soda, and salt for about 30 seconds, ensuring they’re fully combined. Set aside.

In a separate small bowl, mix the buttermilk, vegetable oil, and vanilla extract, and set this mixture aside.

In the bowl of a stand mixer, beat the softened butter at medium speed until smooth. Gradually add the sugar, continuing to beat until the mixture becomes light, fluffy, and pale in color, about 3-5 minutes.

One at a time, add the eggs to the mixture, beating well between each addition until the yolk fully disappears.

Begin alternating between adding the dry flour mixture and the wet buttermilk mixture to the butter and sugar. Start with the dry ingredients and end with the dry, in three portions of dry ingredients and two portions of wet. Be careful not to overmix or exceed medium speed.

Evenly divide the cake batter between the two prepared pans. Smooth the tops and bake for 25-35 minutes, or until a toothpick inserted in the center comes out with just a few moist crumbs attached.

Allow the cakes to cool in their pans for about 10 minutes before turning them out onto a wire rack to cool completely.

In a medium bowl, whisk the egg yolks together and set them aside.

In a medium saucepan, combine the sugar, cornstarch, and salt. Gradually whisk in the milk, making sure everything is thoroughly mixed. Place over medium heat and stir continuously to dissolve the sugar.

Bring the mixture to a gentle simmer. Remove from the heat and slowly temper the egg yolks by adding ¼ to ½ cup of the hot mixture into the bowl of yolks while whisking vigorously. This will prevent curdling.

Pour the tempered yolk mixture back into the saucepan, whisking constantly, and return to heat. Cook for 3-4 minutes, continuing to whisk, until the cream thickens. Once thickened, remove from heat and stir in the vanilla extract.

Transfer the pastry cream to a shallow, heatproof dish. Press plastic wrap directly onto the surface to prevent a skin from forming and refrigerate until completely chilled before using.

Place the chocolate in a microwave-safe bowl.

Pour the heavy cream over the chocolate, and microwave for 30 seconds. Stir and microwave again for another 30 seconds.

Stir until the chocolate is fully melted and the mixture becomes smooth and silky. If needed, continue microwaving in 10-15 second intervals, stirring after each, until the chocolate has fully melted.

Let the ganache cool for about 15 minutes, allowing it to thicken slightly. The ganache should be cool but still pourable when applied to the cake. If it becomes too thick, reheat in short increments in the microwave to loosen it up.

Place one layer of cake onto your serving platter. Spread a generous amount of pastry cream over the top.

Add the second cake layer on top. Use an offset spatula to fill any gaps between the layers with more pastry cream.

Optionally, apply a thin, transparent layer of pastry cream around the sides of the cake. This seals in moisture and gives the cake a "naked" appearance.

Spoon the chocolate ganache over the top of the cake, spreading it evenly. Use an offset spatula to gently push some of the ganache over the edges for a natural, drippy look.

Chill the cake in the refrigerator until an hour or so before serving. This allows all the flavors to meld together perfectly.